The present invention relates to methods and apparatus for increasing the efficiency of a power plant. More particularly, in a power plant having a boiler for heating a fluid (typically water) to form a gaseous phase (typically steam), a power generator for generating electrical power from the gaseous phase, a condenser for partly condensing the gaseous phase to a liquid phase (typically water again) after the gaseous phase has passed through the power generator, a liquid ring vacuum pump for evacuating uncondensed gaseous phase from the condenser, and a chiller for cooling seal liquid (typically water) discharged from the liquid ring pump for re-use in the liquid ring pump, the present invention provides apparatus for utilizing the heat generated during the operation of the chiller to heat a portion of the fluid supplied to the boiler, thereby reducing the amount of heat which must be provided by the boiler in order to form a gaseous phase of the fluid so that electricity can be generated. The heat recovered from the chiller includes the heat generated by (1) vapor condensation in the vacuum pump, (2) gas compression in the vacuum pump, and (3) chiller compression work.
In order to lower the pressure in the condenser of a turbine-driven power plant, previous power plants have used a liquid ring pump to partly evacuate uncondensed steam and leakage air from the condenser. Seal liquid which is discharged from the liquid ring pump is typically cooled and then re-used in the liquid ring pump. Providing the liquid ring pump with cool seal liquid increases the efficiency of the liquid ring pump. As described in U.S. Pat. No. 4,359,313 (which is hereby incorporated by reference herein), the discharged seal liquid can be cooled using a chiller (e.g., a mechanical cooler of the refrigerant evaporative type), the use of which further increases the efficiency of the liquid ring pump because the discharged seal liquid can be cooled to a lower temperature than is possible with a passive system such as one that uses cooling water to absorb heat from the discharged seal liquid. In cooling the seal liquid, the chiller produces heat which, in previous systems, has been carried away by cooling water or dissipated to the air surrounding the chiller.
In order to maximize the efficiency of the power plant, it would be desirable to use the heat generated by the chiller to heat a portion of the fluid delivered to the boiler, thereby reducing the amount of energy which must be provided by the boiler to convert the fluid to a gaseous phase so that electricity may be generated.